Hearing devices are portable hearing apparatuses which are used to supply the hard-of-hearing. To accommodate the numerous individual requirements, different configurations of hearing devices such as behind-the-ear hearing devices (BTE), in-the-ear hearing devices (ITE), e.g. including conch hearing devices or completely-in-the-channel hearing devices (CIC), are provided. The hearing devices designed by way of example are worn on the outer ear or in the auditory canal. Furthermore, bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. In such cases the damaged hearing is stimulated either mechanically or electrically.
Essential components of the hearing devices include in principle an input converter, an amplifier and an output converter. The input converter is generally a receiving transducer, e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output converter is mostly realized as an electroacoustic converter, e.g. a miniature loudspeaker, or as an electromechanical converter, e.g. a bone conduction receiver. The amplifier is usually integrated into a signal processing unit. This basic configuration is shown in the example in FIG. 1 of a behind-the-ear hearing device. One or a number of microphones 2 for recording the ambient sound are incorporated in a hearing device housing 1 to be worn behind the ear. A signal processing unit 3, which is similarly integrated into the hearing device housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker and/or receiver 4, which outputs an acoustic signal. The sound is optionally transmitted to the ear drum of the device wearer via a sound tube, which is fixed with an otoplastic in the auditory canal. The power supply of the hearing device and in particular of the signal processing unit 3 is provided by a battery 5 which is likewise integrated into the hearing device housing 1.
The pulse-density modulation (PDM) or pulse-width modulation (PWM) is frequently used to control the loudspeaker and/or receiver of a hearing device for instance. The digital control is advantageous in that the stage of the digital-analog converter can be dispensed with in the case of digital hearing devices. Digital control circuits also have a significantly higher efficiency rate than analog control circuits. By contrast, analog control circuits are less prone to interference, i.e. they occupy a frequency spectrum which is restricted to an acoustic signal with a small harmonic wave part. The very strongly developed harmonic waves in the case of digital control nevertheless interfere with the wireless transmission of data between hearing devices and the transmission between a hearing device and an external accessory (remote controller, wireless programming device, wireless relay device etc.).
One possible solution to this problem could lie in the following compromise: The receiver is controlled analogously in the case of hearing devices with wireless transmission and in the case of hearing devices without the wireless function, a power-saving digital control takes place. Hearing devices with wireless transmission may however thus not profit from the power-saving digital control.